hi Abe,

I had employed a Copeland "V-line" condensing unit with a scroll in a low temp (-30degF) application, R-404A. the thing has been a screaming nightmare.

Due to the low suction pressure, pump down has been hard to regulate. after a pump-down, discharge gas would backflow into the suction line and the machine would start short-cycling.

During the course of the past several years that it has been in service, we have relocated the discharge line check valve closer to the compressor in order to decrease the volume of gas that will bleed back into the suction (causing the low pressure control to short-cycle), and even had a compressor replacement in the system (which I beleive was related to the pump-down scenario). It finally got to the point that we installed a delay-on-make relay in the contactor circuit to keep the thing from self-distructing on pump down, and called it good.

Personally, I'll never install another scroll in a system which employs pump-down. They ruined me!